Circuit packs, which generally comprise a printed circuit board and a plate, are commonly used in large scale circuitry systems such as switching systems, telephone central offices, and the like in the form of plug in modules or cards. The face plate is usually mounted at one end of the board, in a plane at fight angles to the board, and has indicators, most often lights, to indicate the operative or maintenance conditions of the board. Thus, when a multiplicity of boards or cards are plugged into a carrier or rack thus forming an array, each of the boards can be monitored by the operator by observing the optical indications on or in the corresponding face plate. The optical indicators are usually in the form of light emitting diodes (LED's) mounted on the boards and connected to the circuitry thereof. In order that the LED's can be observed by observing the face plate, the diode leads are bent at right angles and the LED's are inserted into holes in the face plate. Such an arrangement is adequate for use with "through hole" type circuit boards, where the LED leads are soldered in holes in the board, but the LED's overhang the edges of the board prior to the face plate being mounted thereto. This overhang makes the LED's liable to damage in handling, hence, care must be exercised to protect the overhanging diodes prior to final assembly.
A more efficient and economical circuit board arrangement is the so called "surface mount", wherein the various circuit components, including the LED's, are mounted on the surface of the board, without the necessity of through holes in the board. The surface mount arrangement has numerous advantages, such as a more efficient use of available board space, and the elimination of hand mounting those elements, such as the LED's, having leads that must be threaded into the through holes. In addition, the elements mounted on the board surface, and also other circuit connections, are soldered in place by infra-red heating of the entire board. Thus, the surface mounted arrangement is amenable to an entirely automated process, thereby drastically reducing the member of manual operations involved. Unfortunately, the automated process of soldering surface mount components to the board requires that the LED be able to withstand the high temperatures of the infrared heating. In general, an LED for through hole mounting is encapsulated in an epoxy member through which the leads extend, and which functions as a lens for the diode. Under infra-red heating, it is not uncommon for the encapsulation to flow or move, which tends to bend, severely displace, or even break the leads. Thus, the common, commercially available LED is one of two types; the encapsulated type with leads, which is liable to damage in the infra-red soldering operation, and the surface mount type, which is not encapsulated and which can withstand the infra-red heating without damage. In an automated process, the surface mount type is much to be preferred inasmuch as it can be placed and soldered by machine in a much more economical operation than the mounting of the encapsulated lead type. In addition, the surface mounted LED does not overhang the edge of the circuit board, hence, it is not as likely to be damaged in handling.
The surface mounted LED presents another problem, however, and that is how to transmit its upwardly directed light into or through the face plate for viewing. There have been numerous proposed solutions to this problem, one of which, for example, comprises a right angled light guide and an LED encapsulated in a plastic housing. The housing, however, prevents or inhibits repair or replacement or a faulty LED, it being necessary to replace the entire assembly when replacing a faulty diode.